Method and system for reduced v2x receiver processing load using certificates

ABSTRACT

A method at a computing device within an Intelligent Transportation System, the method comprising: determining, at the computing device, whether a short-term certificate is available to sign a message; if the short-term certificate is available, signing the message with a private key associated with the short-term certificate; if the short-term certificate is not available, signing the message with a private key associated with a long-term certificate; and sending the message to a recipient.

FIELD OF THE DISCLOSURE

The present disclosure relates to intelligent transportation systems(ITS) and, in particular, relates to communication between ITS stations.

BACKGROUND

Intelligent transport systems are systems in which a plurality ofdevices communicate to allow for the transportation system to makebetter informed decisions with regard to transportation and trafficmanagement, as well as allowing for safer and more coordinateddecision-making. ITS system components may be provided within vehicles,as part of the fixed infrastructure such as on bridges or atintersections, and for other users of the transportation systemsincluding pedestrians or bicyclists.

ITS system deployment is receiving significant focus in many marketsaround the world, with radiofrequency bands being allocated for thecommunications. In addition to vehicle to vehicle communications forsafety critical and non-critical applications, further enhancements arebeing developed for vehicle to infrastructure and vehicle to portablecommunications.

An ITS station is any entity that may provide ITS communications,including vehicles, infrastructure components, mobile devices, amongother options. In some cases, such ITS station may transmit erroneousdata, either willfully or unintentionally. For example, an ITS stationmay have a faulty sensor which may provide faulty data in ITS messaging.In other cases, a malicious user may insert false information inmessages that would cause the intelligent transportation system to workincorrectly. Typically, when such behavior is detected, an identifier ofone or more certificates of the misbehaving ITS station may be indicatedon a Certificate Revocation List (CRL), which may be used to managemisbehaving ITS stations. An ITS station that receives a message fromanother ITS station having a certificate indicated by the CRL can theneither ignore such message or discount the significance of theinformation within such message.

However, the use of CRLs to manage misbehaving ITS endpoints hasdrawbacks. Specifically, the processing burden on ITS stations may besignificant, especially in areas with a large number of ITS stations.For example, an ITS station on a busy street may receive one thousandmessages each second, and currently a certificate associated with eachmessage would need to be checked against a CRL. Further, to store a CRLfor a large number of ITS stations within a geographic area couldrequire significant resources.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood with reference to thedrawings, in which:

FIG. 1 is block diagram of an intelligent transportation system;

FIG. 2 is a data flow diagram showing a process for verifying messagesbetween a sending ITS station and a receiving ITS station;

FIG. 3 is a block diagram showing logical roles in a security credentialmanagement system;

FIG. 4 is a block diagram showing a first vehicle sending long-livedcertificates and a second vehicle sending short-lived certificates to areceiving ITS station;

FIG. 5 is a process diagram for a process at a sending ITS station fordetermining whether to send a message signed with a short-livedcertificate or a long-lived certificate;

FIG. 6 is a process diagram showing a process at a single mode ITSstation for sending a V2X message;

FIG. 7 is a process diagram showing a process at a receiving ITS stationfor determining whether to perform a CRL check on an incoming V2Xmessage;

FIG. 8 is a process diagram showing a process at a receiving single modeITS station for processing and incoming the 2X message, regardless ofwhether a short or long-lived certificate was used;

FIG. 9 is a process diagram showing a process at a sending ITS stationfor determining whether to send a message with an OCSP staple or not;

FIG. 10 is a process diagram showing a process at a receiving ITSstation for determining whether to perform a CRL check on an incomingV2X message based on the presence of an OCSP staple;

FIG. 11 is a data flow diagram showing an ITS station requesting andreceiving from an OCSP responder the status of a certificate;

FIG. 12 is a timing diagram showing the timing for receiving OCSPstaples in one example embodiment;

FIG. 13 is a block diagram showing a 20 minute window used to obtainOCSP staples; and

FIG. 14 is a block diagram of an example computing device capable ofbeing used with the embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure provides a method at a computing device within anIntelligent Transportation System, the method comprising: determining,at the computing device, whether a short-term certificate is availableto sign a message; if the short-term certificate is available, signingthe message with a private key associated with the short-termcertificate; if the short-term certificate is not available, signing themessage with a private key associated with a long-term certificate; andsending the message to a recipient.

The present disclosure further provides a computing device within anIntelligent Transportation System, the computing device comprising: aprocessor; and a communications subsystem, wherein the computing deviceis configured to: determine whether a short-term certificate isavailable to sign a message; if the short-term certificate is available,signing the message with a private key associated with the short-termcertificate; if the short-term certificate is not available, signing themessage with a private key associated with a long-term certificate; andsending the message to a recipient.

The present disclosure further provides a computer readable medium forstoring instruction code, which, when executed by a processor of acomputing device within an Intelligent Transportation System cause thecomputing device to: determine whether a short-term certificate isavailable to sign a message; if the short-term certificate is available,signing the message with a private key associated with the short-termcertificate; if the short-term certificate is not available, signing themessage with a private key associated with a long-term certificate; andsending the message to a recipient.

In the embodiments described below, the following terminology may havethe following meaning, as provided in Table 1.

TABLE 1 Terminology Term Brief Description ITS Station A communicationdevice associated with the ITS system. In particular, an IntelligentTransport System endpoint which generates or receives V2X messages. AnITS station may for example be associated with a road user such as acar, truck, motorcycle, cyclist, pedestrian, animal, or with a road sideunit. Road user Vehicle, truck, lorry, motorbike, cyclist, pedestrian,animal Road Side Unit A unit in, on, or around a road or other area thatmay be used by vehicles or other road users that may generate and/orread V2X messages. V2X capable vehicle A vehicular ITS Station

Intelligent Transportation System software and communication systems aredesigned to enhance road safety and road traffic efficiency. Suchsystems include vehicle to/from vehicle (V2V) communications, vehicleto/from infrastructure (V2I) communications, vehicle to/from network(V2N) communications, and vehicle to/from the pedestrian or portable(V2P) communications. The communications from a vehicle to/from any ofthe above may be generally referred to as V2X. Further, other elementsmay communicate with each other. Thus, systems may include portableto/from infrastructure (P2I) communications, infrastructure toinfrastructure (I2I) communications, portable to portable (P2P)communications, among others. As used herein, V2X thus includes anycommunication between an ITS station and another ITS station, where thestation may be associated with a vehicle, road side unit, networkelement, pedestrian, cyclist, animal, among other options.

Such communications allow the components of the transportation system tocommunicate with each other. For example, vehicles on a highway maycommunicate with each other, allowing a first vehicle to send a messageto one or more other vehicles to indicate that it is braking, therebyallowing vehicles to follow each other more closely.

Communications may further allow for potential collision detection andallow a vehicle with such a device to take action to avoid a collision,such as braking or swerving. For example, an active safety system on avehicle may take input from sensors such as cameras, radar, LIDAR, andV2X, and may act on them by steering or braking, overriding oraugmenting the actions of the human driver or facilitating autonomousdriving where a human is not involved at all. Another type of advanceddriver assistance system (ADAS) is a passive safety system that provideswarning signals to a human driver to take actions. Both active andpassive safety ADAS systems may take input from V2X and ITS systems.

In other cases, fixed infrastructure may give an alert to approachingvehicles that they are about to enter a dangerous intersection or alertvehicles to other vehicles or pedestrians approaching the intersection.This alert can include the state of signals at the intersection (signalphase and timing (SPaT)) as well as position of vehicles or pedestriansor hazards in the intersection. Other examples of ITS communicationswould be known to those skilled in the art.

Reference is now made to FIG. 1, which shows one example of an ITSstation, as described in the European Telecommunications StandardsInstitute (ETSI) European Standard (EN) 302665, “Intelligent TransportSystems (ITS); communications architecture”, as for example provided forin version 1.1.1, September 2010.

In the embodiment of FIG. 1, a vehicle 110 includes a vehicle ITSsub-system 112. Vehicle ITS sub-system 112 may, in some cases,communicate with an in-vehicle network 114. The in-vehicle network 114may receive inputs from various electronic control unit (ECUs) 116 or118 in the environment of FIG. 1.

Vehicle ITS sub-system 112 may include a vehicle ITS gateway 120 whichprovides functionality to connect to the in-vehicle network 114.

Vehicle ITS sub-system 112 may further have an ITS-S host 122 whichcontains ITS applications and functionality needed for such ITSapplications.

Further, an ITS-S router 124 provides the functionality to interconnectdifferent ITS protocol stacks, for example at layer 3. ITS-S router 124may be capable of converting protocols, for example for the ITS-S host122.

Further, the ITS system of FIG. 1 may include a personal ITS sub-system130, which may provide application and communication functionalities ofITS communications (ITSC) in handheld or portable devices, such aspersonal digital assistants (PDAs) mobile phones, user equipment, amongother such devices.

A further component of the ITS system shown in the example of FIG. 1includes a roadside ITS sub-system 140, which may contain roadside ITSstations which may be deployed on bridges, traffic lights, among otheroptions.

The roadside sub-system 140 includes a roadside ITS station 142 whichincludes a roadside ITS gateway 144. Such gateway may connect theroadside ITS station 142 with proprietary roadside networks 146.

A roadside ITS station may further include an ITS-S host 150 whichcontains ITS-S applications and the functionalities needed for suchapplications.

The roadside ITS station 142 may further include an ITS-S router 152,which provides the interconnection of different ITS protocol stacks, forexample at layer 3.

The ITS station 142 may further include an ITS-S border router 154,which may provide for the interconnection of two protocol stacks, but inthis case with an external network.

A further component of the ITS system in the example of FIG. 1 includesa central ITS sub-system 160 which includes a central ITS stationinternal network 162.

Central ITS station internal network 162 includes a central ITS gateway164, a central ITS-S host 166 and a ITS-S border router 168. Gateway164, central ITS-S host 166 and ITS border router 168 have similarfunctionality to the gateway 144, ITS host 150 and ITS-S border router154 of the roadside ITS station 142.

Communications between the various components may occur through a ITSpeer-to-peer communications network or via network infrastructure 170.

From FIG. 1 above, V2X communications may be used for both road safetyand for improving efficiency of road transportation, including movementof vehicles, reduced fuel consumption, among other factors.

V2X messages are defined by the European Telecommunications StandardsInstitute (ETSI) fall into two categories, namely Cooperative AwarenessMessage (CAM) and Decentralized Environmental Notification Message(DENM). A CAM message is a periodic, time triggered message which mayprovide status information to neighboring ITS stations. The broadcast istypically over a single hop and the status information may include astation type, position, speed, heading, among other options. Optionalfields in a CAM message may include information to indicate whether theITS station is associated with roadworks, rescue vehicles, or a vehicletransporting dangerous goods, among other such information.

Typically, a CAM message is transmitted between 1 and 10 times persecond.

A DENM message is an event triggered message that is sent only when atrigger condition is met. For example, such trigger may be a road hazardor an abnormal traffic condition. A DENM message is broadcast to anassigned relevance area via geo-networking. It may be transported overseveral wireless hops and event information may include details aboutthe causing event, detection time, event position, event speed, heading,among other factors. DENM messages may be sent, for example, up to 20times per second over a duration of several seconds.

Similar concepts apply to the Dedicated Short Range Communications(DSRC)/Wireless Access In Vehicular Environments (WAVE) system in whicha Basic Safety Message is specified instead of the CAM/DENM messagingfrom ETSI.

Security in V2X

In V2X communications, there are various security challenges that needto be overcome. A first challenge concerns trust between the ITSstations. In particular, an ITS station may deliberately orunintentionally send out messages with incorrect content. Unintentionalmessaging may, for example, be based on sensor faults, among otheroptions.

Receiving ITS stations would typically want to avoid acting on incorrectmessages. Thus, a vehicle receiving an incorrect ITS message may, forexample, unnecessarily apply its brakes, move over, among other options,thereby causing traffic problems. In some cases, this may be overcome bydoing plausibility checks on information received in V2X messages andcomparing such information with information received from other sensorssuch as video cameras, lidar, radar, among other options. However, thisis not always possible.

A further security challenge in V2X deals with privacy. In particular,no single entity should be able to track a vehicle merely through V2Xmessaging. Thus, road users should be unable to track one another and,further, in some jurisdictions, operators of a Security CredentialManagement System (SCMS) or wireless network operators should also beunable to track road users.

A further security challenge for V2X is integrity and replay protection.In particular, messages should be unable to be tampered with, forexample utilizing a “man in the middle” attack. Messages previouslytransmitted and replayed should be detected.

A further consideration for security in V2X is non-repudiation. Forexample, if an accident occurs, senders of messages should not be ableto deny that they sent such messages. This is especially true if suchmessages may be directly or indirectly causal in the accident.

Based on the above, A Security Credential Management System has been,and continues to be, developed. The system involves a number of parties,including the Crash Avoidance Metrics Program (CAMP) industryconsortium, the United States Department of Transportation, the UnitedStates National Highway Traffic Safety Administration, Institute forElectrical and Electronics Engineers (IEEE), and the Society forAutomobile Engineers (SAE). Such groups have created a solution based onIEEE 1609, which is a series of standards for dedicated short rangecommunications, as well as IEEE 802.11p with V2X application layerspecifications provided by SAE. Security aspects are standardized inIEEE 1609.2. The solution sometimes goes by the name of DSRC/WAVE.

CAMP have further defined an SCMS that is influencing both proof ofconcept pilots and work in various standards. Such security work isoutlined in general below.

In particular, in a first aspect of security, a V2X message has aparticular format. Typically, the V2X message comprises three mainparts. The first part is the application message content. The secondpart is the signature of the message provided by the sending ITSstation. The third part of the V2X message is a certificate which issigned by a certificate authority.

CAMP uses elliptic curve Qu-Vanstone (ECQV) implicit certificates forV2X communication as specified in IEEE 1609.2, “IEEE Standard forWireless Access in Vehicular Environments—Security Services forApplications and Management Messages”, and are known to those skilled inthe art.

During use, the sender would sign the V2X message contents using itsprivate key and send the signed message along with its ECQV certificatesto the recipient. The recipient then calculates the sender'sverification public key from the ECQV certificate and the certificateauthority's public key. The calculated public key can now be used toverify the signed message.

A vehicle or other ITS station could send a message signed with one ofits private keys, referred to as a, and the corresponding implicitcertificate, including for example (P, info) to the recipient ITSstation. In the above, P is the public reconstruction key and info isthe administrative information. The recipient extracts the sender'spublic verification key by calculating eP+D, where e=hash(info,P) and Dis a trusted copy of the certificate authority's public verificationkey,

The receiver then uses the sender's public verification key to verifythe signature on the message. This is for example illustrated in FIG. 2.

Referring to FIG. 2, a sending ITS station 210 first forms a message atblock 212. The sending ITS station then signs the message with anappropriate key a, shown by block 214.

The sending ITS station 210 then sends the message, its signature s, andthe corresponding ECQV certificate (P, info) as shown by block 220.

The receiving ITS station 230 may then check a certificate revocationlist for the presence of the certificate, as shown at block 240. Thecertificate revocation list is described in more detail below. If thecertificate is on the revocation list, the receiving ITS station may,for example, discard the message and end the process (not shown).

If the certificate is not on the revocation list, the receiving ITSstation 230 may then extract the public verification key A=eP+D. This isshown at block 242.

The receiving ITS station 230 may then verify S with A, as shown atblock 244.

One issue with the above is that a vehicle with a single staticcertificate could be tracked by infrastructure network elements or byother road users. To avoid this, an ITS station may be assigned a numberof certificates for a certain time period, after which such certificatesare discarded. For example, a vehicle or other ITS station may beassigned twenty certificates within a given week, after which thecertificates are discarded.

An ITS station may cycle through the certificates, using each one onlyfor a certain time period before another certificate is used instead.For example, each certificate may be used for five minutes, after whichthe next certificate is used. Each certificate further may include adifferent pseudonym as an identifier. Such use of rotating certificatesmay prevent the tracking of the vehicle by infrastructure elements.

Misbehavior Authority

A Misbehavior Authority (MA) determines whether messages from an ITSstation are trustworthy. If the Misbehavior Authority determines that anITS station can no longer be trusted then the ITS station certificatesare revoked.

In this way, recipients of the V2X messages may be able to check whetherthe received certificate is still valid and has not been revoked. Thisis typically done by putting certificate identifiers of roguecertificates on a certificate revocation list.

However, such certificate revocation lists may become very large. Eachvehicle is issued with approximately 20 certificates per week and may beissued with many years' worth of certificates. In this regard, eachvehicle or ITS station that has its certificates revoked would add manycertificates to such certificate revocation list.

Further, a geographic region for CRLs is generally large, leading tomany ITS stations potentially being on the list.

In order to overcome this, CAMP has decided to use hash chains. A hashchain starts with a seed value and hashes it, and then hashes this hash,then hashes this hash and so on. The result is a sequence of values,called linkage seeds, each of which is the hash of the previous linkageseed. Linkage values may be generated from the linkage seeds.

When generating the ECQV certificates, the certificate authority placesthe k^(th) linkage value (or a portion thereof) from at least onelinkage-generating entity in the administrative portion of thecertificate governing the k^(th) time usage. To revoke an ITS station,the misbehavior authority places the current linkage seed in the CRL.

A recipient can quickly calculate the appropriate linkage valueassociated with a linkage seed on the CRL and compare it with thelinkage value in the certificate. If the linkage values match, thecertificate and its associated V2X message is rejected.

ITS stations can compute the linkage values associated with each linkageseed on the CRL on a weekly basis and save them in memory.

The above description is however simplified. CAMP requires two sets ofhash chains for privacy reasons. Each generally utilizes the abovebehaviour.

In CAMP, linkage values are generated by two Link Authorities (LA1 andLA2). Each generates a random linkage seed per ITS station, Is₁(0) andIs₂(0), respectively. The linkage authorities then generate linkageseeds iteratively for subsequent times i, Is₁(i) and Is₂(i),respectively, where i corresponds to a number for a week.

Linkage values are generated from these linkage seeds and are placedwithin the ECQV certificates. Two different linkage values are providedfor each of the certificates that a vehicle may use within the givenweek. For time value (i,j), LA1 calculates the value plv₁(i,j) as afunction of ID_(LA1), Is₁(i), and j using AES and XOR, where ID_(LA1) isa value identifying LA1. In this case, j corresponds with a givencertificate that is used within the week i.

More specifically, the first linkage seed is used as a key in an AESoperation to produce a set of bits which is XOR'd with the equivalentset of bits provided using the 2^(nd) linkage value, and this is what isprovided in the certificate by the transmitting ITS stations. Suchoperations are performed by the certificate authority.

For each misbehaving ITS station, the CRL contains two linkage seeds,one from each link authority, from which the receiving vehicle cangenerate all possible linkage value pairs that might potentially be usedby that misbehaving vehicle at any given time during that week orsubsequent weeks. The vehicle receiving the V2X message performs thesame AES and XOR operations as described above on the linkage valuepairs derived from the linkage seed information in the CRL.

By comparing this sequence with the sequence received in thecertificate, the V2X message receiving ITS station can determine whethera message should be discarded because it is sent by an untrustworthyvehicle.

With this system, neither link authority can track a particular vehiclewithout colluding with the other link authority.

Based on the above principles, a CAMP system architecture is describedwith regard to FIG. 3.

In particular, the embodiment of FIG. 3 provides a structure in which atleast two logical roles need to collude in order to obtain enoughinformation to track a vehicle and hence to mitigate againstunauthorized collusion these two logical roles can be carried out bydifferent organizations.

In the embodiment of FIG. 3, the SCMS manager 310 sets the misbehaviorrevocation policy, shown at block 312.

The device configuration manager 320 provides SCMS configurationinformation to various devices 322. For example, the deviceconfiguration manager 320 may provide network addresses, changes innetwork element certificates, among other information.

The enrolment certificate authority 324 issues enrollment certificatesto the device, which the device can then use for obtaining pseudonymcertificates, among other information. Further, different enrolmentcertificate authorities may issue enrolment certificates for differentgeographic regions, manufacturers or device types.

A linkage authority, such as linkage authorities 330 and 332, generateslinkage values that are used in the certificates and support certificaterevocation. The use of two linkage authorities prevents an operator of asingle linkage authority from linking certificates belonging to aparticular device and thereby prevents a single linkage authority fromtracking devices.

A location obscurer proxy 334 changes device source address and preventsthe linking of network addresses to location.

A misbehavior authority 340 determines which devices are misbehavingaccording to reports that it receives, and enters such devices on ablacklist managed by internal blacklist manager 342 and on the CRL,managed by CRL generator 344. The detection of misbehavior is donethrough a global detection module 346.

A pseudonym certificate authority 350 issues pseudonym certificates todevices, each certificate only being usable over a limited and specifiedtime. Pseudonym certificate authorities may be limited to use for aparticular geographic region, used by a particular manufacturer or usedby a particular device type.

The registration authority 360 validates, processes and forwardsrequests for pseudonym certificates to the pseudonym certificateauthority 350.

An intermediate certificate authority 370 is part of a chain of trustback to the Root CA 372 that enables the intermediate CA to issuecertificates on behalf of the Root CA 372. A Root certificate authority372 is a trusted entity which issues certificates that can be used toverify information or identity provided by the sender of thecertificate. The Root CA may be managed by a root management function374.

Certificates are, for example, defined in the IEEE 1609.2-2016 standardfor Wireless Access in Vehicular Environments—Security Services forApplications and Management Messages. An example of a certificate formatis that described by IEEE 1609-2.

In IEEE 1609.2, two forms of revocation information are possible. Thetype of revocation information that applies to certificate is indicatedby a certificateID field in a certificate.

A first form of revocation information is linkage based. If thecertificateID field indicates the choice linkageData, the certificate isrevoked by publishing the linkage seed value corresponding to thelinkageData value. This is for example provided in IEEE 1609.2.

A second form of revocation information may be hash ID-based. In thiscase, if the certificateID field indicates the choice name, binaryID ornone, the certificate may be revoked by publishing a hash of thecertificate. This is for example described in IEEE 1609.2 specification.

Further, in some cases, the certificate itself may provide an indicationthat it will not appear on a CRL. Specifically, in section 5.1.3.3 ofthe IEEE 1609.2 specification, one way in which a receiver of thecertificate can be informed whether or not the certificate will berevoked and specifically whether or not it will ever appear on acertificate revocation list is provided. In particular, this sectionstates:

a cracaId of all 0s and a CRLSeries value of 0 indicates is that thecertificate will not be revoked, i.e., that there is no revocation listthat it will appear on. This may be because it has a very short lifetimeor for some other reason.

Thus, from the above, the cracaId is one of the fields that is includedin a certificate.

A CRL may have various contents as for example described in IEEE 1609.2.

Online Certificate Status Protocol (OCSP) and OCSP Stapling

OCSP is a client-server protocol that is used by a client for obtainingthe revocation status of the digital certificate from a server. Forexample, OCSP is defined in the Internet Engineering Task Force (IETF)Request For Consultation (RFC) 6960, “X.509 Internet Public KeyInfrastructure Online Certificate Status Protocol—OCSP”, June 2013.

The certificate being your revoked may, for example, be an X.509 digitalcertificate in some cases.

Upon receiving the digital certificate, for example as part of a signedmessage, an OCSP client queries and OCSP server to determine if thecertificate is valid and has not been revoked.

According to IETF RFC 6066, “Transport Layer Security (TLS) Extensions:Extension Definitions”, January 2011, the OCSP server may then providean OCSP response indicating one of the following states of the receivedcertificate: Good, Revoked, Unknown.

The OCSP server may also include other information, including a“thisUpdate” field and a “nextUpdate” field, similar to fields containedin CRLs. This other information together provides a start and endtime/date of the validity of the OCSP response. In other words, thefields define a period of validity of the OCSP response.

The OCSP server may alternatively provide an error, for example based ona malformed OCSP request.

OCSP stapling is also known as “TLS certificate status requestextension”. This may, for example, be defined in IETF RFC 6066 and alsoIETF RFC 6961, “The Transport Layer Security (TLS) Multiple CertificateStatus Request Extension”, June 2013.

OCSP stapling modifies OCSP in that instead of an entity that receives acertificate having to contact the OCSP server, the entity that intendsto send a certificate first contacts an OCSP server using theabove-described mechanism, receives a time-stamped OCSP response, andthen appends or “staples” the time stamped OCSP response to thecertificate that it sends out. The appended/stapled time stamped OCSPresponse proves to all receiving entities that the received certificateis valid for a specific period of validity. In other words, thecertificate has not been revoked.

Stapling therefore negates the requirement for clients receiving digitalcertificate or data signed by a digital certificate to contact thecertificate authority that issued the certificate using OCSP themselves,or indeed to check the received certificate against a CRL.

IETF RFC 6066 describes more details of messaging that is used as partof the TLS mechanism in a typical case of a web client accessing aserver. During the TLS handshake, the web client may request the serverto provide an OCSP response, which the server staples to the certificatethat the server provides to the client. The client makes this request byincluding a CertificateStatusRequest in the TLS handshake.

The contents of an OCSP response are defined in IETF RFC 6960.

The contents of a regular OCSP request are also defined in IETF RFC6960.

Based on the above, the use of CRLs to manage misbehaving vehicles orV2X endpoints has drawbacks based on various factors.

A first factor may be the length of the CRLs, which can be very large.In particular, a CRL may pertain to a very large geographic area andthere may be many vehicles in such geographic area. Further, there maybe multiple CRLs per ITS station or service type and this may lead to anumber of large CRLs that may be required to be searched prior toidentifying misbehaving vehicles.

The use of large CRLs can be onerous for both processing and in terms ofmemory for ITS stations that are the recipients of V2X messages. EachITS station has to compare an identifier of the certificate of eachreceived message with the identity of all certificates indicated by theCRL. The comparing would determine whether the message could be trusted.

For example, in an urban environment, an ITS station could receivearound 1000 signed messages each second, based on 100 vehicles or ITSstations in proximity to each other, where each ITS station is sending10 messages per second. This may, for example, be Basic SafetyMessaging.

Additionally, there may be potentially wasted cellular resources inprovisioning large CRLs or sets of CRLs to ITS stations.

Based on this, in accordance with the embodiments of the presentdisclosure, a certificate may be provided for a V2X message whichcontains an indication to a receiving ITS station that a check of theCRL does not need to be performed. The indication may, for example, bethe use of a short-lived certificate, which provides the indication thatthe certificate is still valid since the validity period is short-lived.The indication may further be an OCSP staple attached to a certificate,indicating that a check of the certificate against the CRL was performedrecently and that the certificate is still valid.

In any of the above embodiments, the processing at the receiving ITSstation can be reduced by not requiring the CRL check for such V2Xmessages. Further, the storage requirements on the receiving ITS stationcan be reduced, since the CRL may not be as long.

Each scenario is described below.

Combined Use of Short-Lived Certificates and Long-Lived Certificates

A vehicle or other ITS station may send V2X communications signed by acertificate. In accordance with one embodiment of the presentdisclosure, a vehicle may sign the V2X message with either short-livedor long-lived certificates, depending on a variety of factors.

Reference is now made to FIG. 4. In accordance with the embodiment ofFIG. 4, a vehicle 410, and specifically a computing device 412 onvehicle 410, may not have regular WAN connectivity (for example usingcellular or WLAN).

A vehicle 414, and specifically a computing device 416 on vehicle 414,may have regular WAN connectivity (for example using cellular or WLAN),for example from a base station or access point 418.

Each of computing devices 412 and 414 may determine whether to send ashort-lived certificate or a long-lived certificate based on variousfactors. The computing device on each vehicle may decide whether it hasthe capability to obtain short-lived certificates 420. If it does nothave the capability to obtain such certificate, the vehicle will alwayssend long-lived certificates 430.

If a computing device 416 for vehicle 414 does have the capability toobtain short-lived certificates, then computing device 416 will use oneof its short-lived certificates 420 when sending a message body 422 ifsuch certificate is available and the certificates have not yet expiredin time. If there are no short-lived certificates and the short-livedcertificates that exist are already expired, the computing device 416will use one of its long-lived certificates when sending message body432.

Optionally, new information in a certificate that is sent in a V2Xmessage, as shown by area 424, may be used by receiving vehicle 440, andspecifically a computing device 442 associated with vehicle 440, todetermine whether the receiving vehicle 440 can avoid doing a checkagainst the CRL.

While the embodiment of FIG. 4 only shows area 424 in the short livedcertificate 420, in some cases new information may also be shown withregards to a long lived certificate 430.

In the case of a V2X message received by vehicle 440 from vehicle 414,since new information associated with the certificate is present andindicates that the certificate is a short-lived certificate, it isnecessary for the computing device 442 associated with the receivingvehicle 440 to check that the certificates are valid, but no checkagainst the CRL is needed.

In the case of a V2X message from vehicle 410 to vehicle 440 that uses along-lived certificate, since there is no indication in the certificatethat the certificate is short-lived, a check against a CRL is needed.

Various reasons exist for the inability to obtain short-livedcertificates. In one embodiment, a vehicle may not be cellular enabled,and therefore may not be regularly connected to a server which mayprovide short-lived certificates. In this case, the vehicle may rely onthe long-lived certificates that may be downloaded at longer intervals,for example when the vehicle is serviced, among other options.

However, as the number of vehicles that are connected via cellularincreases in the future, then number of vehicles that can frequently getfresh certificates will increase. In this way, processing and memoryrequirements on vehicles which receive V2X messages will decrease.

Utilizing the above, several possible ITS station deployment scenariosexist. For example, these are provided in Table 2 below.

TABLE 2 Indicating ITS station deployment scenarios in a particulargeographical region Dual ITS Single Single mode ITS station mode ITSmode ITS station type: deployment station type: station type:short-lived and scenario long-lived short-lived long-lived number certsonly certs only certs Notes 1 x x Y x Y x legacy method 2 x Y Y Y x xlegacy method 3 Y x Y 4 Y Y x 5 Y Y Y

In accordance with Table 2 above, various deployment situations exist.In a first ITS deployment scenario, labeled as scenario 1 in Table 2, ahomogenous use of the dual-mode ITS station types may be provided. Inthis deployment scenario, one ITS station type is envisioned,specifically a dual-mode ITS station that can handle both “long-lived”certificates” and “short-live” certificates.

A new batch of short-lived certificates would be obtained frequently.For example, the short-lived certificates may be obtained daily.

In case of temporary network connection unavailability, the ITS stationmay be unable to obtain a new short-lived certificate. In this case, theITS station can fall back on using long-lived certificates to signmessages.

From Table 2 above, a further deployment scenario, labeled as scenario 3in the table, comprises a heterogeneous mix of single mode (long livedcertificate based) ITS station types and dual-mode ITS station types.

The two ITS station types are envisioned and communication between thetwo ITS station types are possible.

In particular, the single mode ITS station type is designed to work in asystem where a batch of long-lived certificates have been provided tothe vehicle. A batch of long-lived certificates refers to a scenario,for example, where three years worth of certificates have been providedto the vehicle. The certificates could, for example, be uploaded to thevehicle at a factory or when the vehicle is serviced for example at agarage. An example of a V2X solution would be one conforming to thecurrent CAMP specification and thus the single mode ITS station mightform part of the first generation of ITS stations.

Further the single mode ITS station is capable of both generating a V2Xmessage that uses one of the long-lived certificates and receiving a V2Xmessage that includes long-lived certificates.

In this scenario, a dual-mode ITS station type is one that can handleboth long-lived and short-lived certificates. This ITS station may formpart of the second generation of ITS station who would obtain a newbatch of short-lived certificates that would be obtained frequently.

While the two scenarios are described above, in other cases, as seenfrom Table 9, other deployment scenarios utilizing a combination ofsingle mode ITS stations and/or a dual mode ITS station type couldequally be used.

In the scenarios above, dual-mode ITS stations should attempt to get anew set of certificates every “short-lived” period. For example, thismay occur every day. Such short-lived certificates could for example beobtained via cellular connectivity in some embodiments. However, inother embodiments other ways of obtaining the certificates may bepossible, including WLAN connections. For example, a vehicle parkedovernight in a garage may have regular access to WiFi. Other options arepossible.

Short-lived certificates are provided from a certificate authority withone or more distinguishing features that enable an endpoint thatreceives the certificate to determine whether the certificate isshort-lived or long-lived. Details of various distinguishing featuresare provided in the embodiments below.

The decision to send a short-lived or long-lived certificate, may forexample, utilize the process of FIG. 5.

Referring to FIG. 5, the process starts at block 510 and proceeds toblock 512 in which a V2X message is generated. Such V2X message mayinclude periodic reports or event reports, among other options.

The process then proceeds to block 520 in which a check is made todetermine whether any non-expired short-lived certificates areavailable. In particular, if the dual-mode ITS station has access tofresh, short-lived certificates that have not yet expired, then it canuse such certificates to send V2X messages. A non-expired certificatewould be one in which the current time is within the validity period ofthe certificate.

From block 520, if there are no non-expired short-lived certificatesthen the process proceeds to block 530 in which the message generated atblock 512 is sent to the recipient utilizing a long-lived certificate.From block 530 the process proceeds to block 540 and ends.

Conversely, from block 520, if there are non-expired short-livedcertificates, the process proceeds to block 550 in which the ITS stationmay send the message generated at block 512 with the short-livedcertificate. From block 550 the process proceeds to block 540 and ends.

Conversely, a single mode ITS station uses traditional legacyprocedures. Referring to FIG. 6, the process at a legacy or single modeITS station starts at block 610 and proceeds to block 612 in which a V2Xmessage is generated.

The process would then proceed to block 620 in which the message is sentwith the long-lived certificate of the ITS station.

The process then proceeds to block 630 and ends.

A receiving ITS station, if capable of the dual-mode perception, maythen be able to determine whether the certificate is short-lived orlong-lived. In particular, reference is now made to FIG. 7, which showsthe process at a receiving ITS station. In particular, the process ofFIG. 7 starts at block 710 and proceeds to block 712 in which the ITSstation receives the V2X message.

The process then proceeds to block 720 in which the certificate isinspected and a check is made to determine whether the certificate is ashort-lived certificate. Details of the checking at block 720 areprovided below.

If the certificate is not a short-lived certificate, the processproceeds to block 730 in which the certificate is designated to be along-lived certificate.

From block 730 the process proceeds to block 732 in which a check ismade to determine whether the certificate is identified on the CRL.Specifically, the ITS station will periodically receive and store a CRL,and the check at block 732 may be made against the CRL to determinewhether the certificate is on it. Such checking may be done inaccordance with the embodiments described above.

If the certificate is identified on the CRL then the process proceedsfrom block 732 to block 740 in which the V2X message is discarded. Fromblock 740 the process proceeds to block 742 and ends.

Conversely, if the certificate is long-lived certificate but not on theCRL, the process proceeds from block 732 to block 750 in which a checkis made to determine whether the certificate is valid and the message iscorrectly signed. If not, the process may proceed to block 740 todiscard the message and the process may then proceed to block 742 andend.

From block 750, if the certificate is verified and the message iscorrectly signed, then the V2X message may be passed to the applicationlayer, shown at block 760. From block 760 the process proceeds to block742 and ends.

From block 720, if the certificate is identified as short-lived then theprocess proceeds to block 770 in which a check is made to determinewhether the certificate is valid and the message is correctly signed. Ifno, then the process proceeds to block 740 in which the message isdiscarded and to block 742 in which the process ends.

Conversely, if the certificate is verified and the message is correctlysigned, as determined at block 770, the process may proceed to block 772in which the message is passed to the application layer. From block 772the process proceeds to block 742 and ends.

Referring to FIG. 8, a single mode ITS station receiving a message wouldperform the same processing on the received message, regardless ofwhether the certificate was a long-lived or a short-lived certificate.In particular, the process of FIG. 8 starts at block 810 and proceeds toblock 812 in which the single mode ITS station receives the V2X message.

From block 812 the process then proceeds to block 820 in which a checkis made to determine if the certificate is on the CRL. As will beappreciated, a short-lived certificate would not be on a CRL, but asingle mode ITS station would still do the check since this would be thelogic for a traditional ITS station.

From block 820, if the certificate is identified to be on the CRL, theprocess proceeds to block 830 in which the message is discarded. Theprocess then proceeds to block 832 and ends.

Conversely, if the message is not on the CRL, the process proceeds toblock 840 in which a check is made to determine whether the certificateis valid and if the message is signed correctly. If not, the processproceeds from block 840 to block 830 in which the message is discarded.The process then proceeds to block 832 and ends.

From block 840, if the certificate is verified and the message iscorrectly signed, then the process proceeds to block 850 in which theV2X message is passed to higher layers.

The embodiments of FIGS. 7 and 8 provide only one option for thereceiving V2X station. In other cases, the ordering of the checks couldbe different. Further, other combinations of checks may also bepossible. A key in the embodiment of FIG. 7 is that for a short-livedcertificate, a check against the CRL is avoided, saving processing timeat the receiving ITS station.

The determination of the certificate type at block 712 may be done in anumber of ways. Examples are provided below.

Determination Of Certificate Type Through Use of Cracaid

In one embodiment, if the certificate authority is issuing a short-livedcertificate, which for example may only have a 24-hour expiry time, thenit may set the cracaid to all zeros. By setting the cracaid to allzeros, this may provide an indication to a receiving ITS station thatthe certificate is a short-lived certificate.

On the other hand, if the certificate authority is issuing a long-livedcertificate, then it will set the cracaid to a nonzero value inaccordance with the IEEE 1609.2-2016, Section 5.1.3.3.

Therefore, the check at block 712 would check the cracaid and therebydetermine whether or not a check against the CRL is required. Thecracaid is trustworthy because it is signed by the root, and notsomething that may be changed by an intermediary.

Determination of Certificate Type Through Linkage Value

In a further embodiment, a specific linkage value or specific linkagevalues may be used in a certificate to indicate that the certificate isa short-lived certificate. This may be standardized, for example, inIEEE 1609.2 in some cases.

For example, a nine byte sequence of all zeros as a linkage value mayindicate a short-lived certificate. In accordance with the presentdisclosure, this specific linkage value (or values) may be called theshort-cert-indicative-linkage-value.

A dual mode ITS station, on reception of the V2X message, would performvarious actions, including checking whether the certificate isauthentic. In other words, the check would indicate whether thecertificate authority provided a signature that is consistent with thecertificate contents.

The check at block 712 may check whether the linkage value in thereceived certificate is equal to theshort-cert-indicative-linkage-value. If it is, and if the message iswithin the validity period, indicating that the certificate is notexpired, and provided that other checks on the V2X message are passed,the check of the CRL is not necessary. From FIG. 7, if the validityperiod has expired for a short-lived certificate then the message isdiscarded.

Conversely, the use of linkage values may find that the linkage value inthe received certificate does not equal theshort-cert-indicative-linkage-value. In this case, the message will beprocessed as a long-lived certificate in a conventional way, where a CRLcheck would be needed.

For the legacy mode ITS station, on reception of the V2X message, themessage would be processed in a manner utilizing legacy CAMP, forexample using the process of FIG. 8. Consequently, if the receivedcertificate happens to be a short-lived certificate and linkage valuehappens to be set to the short-cert-indicative-linkage-value, then asingle mode or legacy ITS station will check that the linkage value isnot indicated by the CRL. In this case, theshort-cert-indicative-linkage-value should never appear on the CRL toensure such certificate is not deemed invalid.

Based on the above, a legacy ITS station will still check the CRL andfind nothing, and hence the certificate will pass the CRL test.

A long-lived certificate would be processed by a legacy ITS station inthe same way that current long-lived certificates are processed using aCAMP procedure.

The use of a linkage value may allow for legacy ITS stations to handlemessages with both short and long-term certificates.

Determination of Certificate Type Through HashID

In a further embodiment, instead of using the linkage value, the IEEE1609.2 standard specifies that HashIDs may be used for revokingcertificates. In this case, when a certain Hash ID value is used in thecertificate, this may indicate that the certificate is a short-livedcertificate and hence no check against the CRL would be needed. Thus asimilar process to that described above with regard to the linkagevalues could be utilized with Hash IDs.

For example, in one case, a certificate may have a 10 byte sequence ofall zeros as the Hash ID, which would indicate that this certificate isshort-lived. Other values may conversely indicate that the certificateis long-lived. The use of a 10 byte sequence of values is however merelyprovided as an example, and other examples of a value for a HashID couldbe used with the embodiments of the present disclosure to indicate ashort-lived certificate.

Determination of Certificate Type Through Validity Period

In a further embodiment, a receiving ITS station may be programmed totreat any non-expired certificate which has a duration X and a starttime that is within X hours of the current time to be short-lived, whileother non-expired certificates are treated as long-lived. For example,the duration X could be 24 hours assuming that a device has to fetch newshort-lived certificates every 24 hours.

In this regard, the check at block 712 may find the duration of thecertificate and determine based on such duration whether the certificateis a short-lived or a long-lived certificate and therefore whether theCRL check needs to be done or not.

Determination of Certificate Types Through Different CertificateAuthorities

In a further embodiment, short-lived certificates may be provided bydifferent certificate issuers than long-lived certificates. An issueris, for example, defined in IEEE 1609.2.

Different issuers could be associated with different root certificateauthority certificates. These different root certificate authoritycertificates could be associated with the same or different certificateauthority organizations.

Further, different issuers within a certificate chain that is descendedfrom the root certificate and the same certificate authority may beused.

The case in which all certificates are managed by the same organizationor certificate authority domain may allow better privacy managementbecause the SCMS entities relevant to the management of both short-livedand long-lived certificates may be managed within the control of thesame certificate authority. Such SCMS entities include, for example, themisbehavior function and CRL issuing network elements and the entitiesresponsible for blacklisting and white listing vehicles.

In one embodiment, two behaviors may be defined for a receiving ITSstation. In one case, devices that receive V2X message would bepreconfigured with an association between an issuer identity andcertificate type, whether short-lived or long-lived. When the ITSreceiving station determines that the certificate is a short-lived type,then it does not perform a check against the CRL. However, when thereceiving ITS station identifies the certificate as a long-lived type,then the CRL check is performed.

In another embodiment, the V2X receiving ITS station would alwaysperform a check against the CRL. However, in this case, the certificateauthority that is associated with the short-lived certificate wouldprovide a CRL with a length of zero. This would enable the benefit ofreduced processing burden at the receiving ITS station to be achieved bya single mode ITS station design that always assumes there is a CRLpresent. This embodiment may therefore be beneficial if legacy ITSstations are deployed which are not explicitly designed to identifyshort-lived certificates and process them in a different way.

SCMS Actions for Dual-Mode Terminals

At the network, identification by the misbehavior authority that avehicle is misbehaving, irrespective of whether the vehicle ismisbehaving using its short-lived certificates or long-livedcertificates, would generally result in an identifier of the long-livedcertificates to be placed on the CRL.

Further, the vehicle may also be blacklisted with regard to the issuanceof new long-lived certificates and the vehicle may further beblacklisted with regard to the issuance of new short-lived certificates(or OCSP staples as described below).

Similarly, when a vehicle finds it has been detected as beingmisbehaving, either because its long-lived certificates have been placedon the CRL or it has been refused allocation of new short-livedcertificates, then a vehicle may take appropriate action with regard tothe usage of other types of certificates. For example, a vehicle couldcompletely stop generating V2X messages and not use any of itscertificates if it has been blacklisted, even if one class ofcertificate is potentially still usable. This may identify the case, forexample, that the vehicle has a faulty sensor but is acting as a goodcitizen within the ITS system.

OCSP Staples

As an alternative embodiment to long and short-lived certificates, in afurther embodiment the scenario may exist where devices only obtainthree years worth of long-lived certificates, but in which regularaccess to the SCMS may be made in order to obtain OCSP responses whichcan then be stapled to the certificates in V2X messages.

A device that receives V2X messages with the OCSP response stapled to itdoes not need to check the CRL, and instead only needs to check that thestapled OCSP response is correctly signed and has not expired. In thisway, the processing burden of the CRL is avoided.

In particular, rather than having to obtain a large number ofshort-lived certificates, the present embodiment may only obtain threeyears' worth of long-lived certificates. Further, the device sending theV2X messages may also regularly access the SCMS in order to obtain OCSPresponses. These responses can be stapled to the certificates in the V2Xmessage, providing an indication to the receiving ITS station that a CRLcheck is not needed.

In particular, reference in now made to FIG. 9, which show a process atan ITS station sending a V2X message. The process of FIG. 9 starts atblock 910 and proceeds to block 912 in which a V2X message is generated.Such V2X message may include periodic reports or event reports, amongother options.

The process then proceeds to block 920 in which a check is made todetermine whether a non-expired OCSP response is available for thecertificate of the ITS station. One embodiment for obtaining OCSPresponses is described below. A non-expired OCSP response would be onein which the expiry time is still in the future.

From block 920, if there is no non-expired OCSP response then theprocess proceeds to block 930 in which the message generated at block912 is sent to the recipient utilizing a long-lived certificate, withoutan OCSP staple. From block 930 the process proceeds to block 940 andends.

Conversely, from block 920, if there is a non-expired OCSP response, theprocess proceeds to block 950 in which the ITS station may send themessage generated at block 912 with the long-lived certificate having anOCSP staple. From block 950 the process proceeds to block 940 and ends.

A receiving ITS station, may then be able to determine whether thecertificate of an incoming message has an OCSP staple. In particular,reference is now made to FIG. 10, which shows the process at a receivingITS station. The process of FIG. 10 starts at block 1010 and proceeds toblock 1012 in which the ITS station receives the V2X message.

The process then proceeds to block 1020 in which a check is made todetermine whether the certificate has an OCSP staple. Details of thechecking at block 1020 are provided below.

If the certificate does not have an OCSP staple, the process proceeds toblock 1032 in which a check is made to determine whether the certificateis identified on the CRL. Specifically, the ITS station willperiodically receive and store a CRL, and the check at block 1032 may bemade against the CRL to determine whether the certificate is on it. Suchchecking may be done in accordance with the embodiments described above.

If the certificate is identified on the CRL then the process proceedsfrom block 1032 to block 1040 in which the V2X message is discarded.From block 1040 the process proceeds to block 1042 and ends.

Conversely, if the certificate is not on the CRL, the process proceedsfrom block 1032 to block 1050 in which a check is made to determinewhether the certificate is verified and the message is correctly signed.If not, the process may proceed to block 1040 to discard the message andthe process may then proceed to block 1042 and end.

From block 1050, if the certificate is verified and the message iscorrectly signed, then the V2X message may be passed to the applicationlayer, shown at block 1060. From block 1060 the process proceeds toblock 1042 and ends.

From block 1020, if the certificate has an OCSP staple then the processproceeds to block 1070 in which a check is made to determine whether thecertificate is verified, including the OCSP staple, and the message iscorrectly signed. If no, then the process proceeds to block 1040 inwhich the message is discarded and to block 1042 in which the processends.

Conversely, if the OCSP staple is valid and the message is correctlysigned, as determined at block 1070, the process may proceed to block1072 in which the message is passed to the application layer. From block1072 the process proceeds to block 1042 and ends.

Therefore, in accordance with the above, an OCSP staple may be added tolong-lived certificates, which may allow a receiving ITS station toavoid doing a CRL check for the received certificate.

The sending ITS station may receive an OCSP response for each of thecertificates that it will use in a particular week. To do this, thesending ITS station may use a linkage value as an identifier. In thiscase, the OCSP response checks to see whether the linkage seedcorresponds to a linkage value that appears on the CRL, and if it doesnot, then the OCSP responder can provide the OCSP response indicatingthat the certificate is good. Otherwise, the responder can provide aresponse indicating that the certificate is revoked or that the statusof the certificate is unknown.

Similarly, if the HashID is used to obtain OCSP responses, the OCSPresponder can check to see whether the HashID received from the ITSstation corresponds to a HashID that appears on the CRL. If not, theresponder can provide an OCSP response saying that the certificate isgood. Otherwise, the responder could provide a response indicating thateither the certificate is revoked or the status of the certificate isunknown.

The check of the certificate with an OCSP responder is illustrated, forexample, utilizing the embodiment of FIG. 11. In the embodiment of FIG.11, the ITS station 1110 can send messages to an OCSP responder 1112.

In particular, the message from the ITS station may be message 1120 andthe response generated by the OCSP Responder may be message 1130.

Message 1120 may contain the linkage value or the Hash ID for one ormore certificates of the ITS station 1110, as described above.

Message 1130 may indicate whether the certificate is valid, revoked orthe status of the certificate is unknown.

In one embodiment, message 1120 may for example be a request as definedin IETF RFC 6960, in section 2.1, and may be in the form provided inTable 3 below.

TABLE 3 Example OCSP Status Request - protocol version - servicerequest - target certificate identifier (e.g. Linkage value or HashID) -optional extensions, which MAY be processed by the OCSP responder

In Table 3 above, the bold insertion shows additional information whichmay be provided in the status request.

Further, message 1130 may be for example be a response as defined inIETF RFC 6960, in section 2.2, and may be in the form provided in Table4 below.

TABLE 4 Example OCSP Status Response The response for each of thecertificates in a request consists of: - target certificate identifier(e.g. Linkage value or HashID) - certificate status value - responsevalidity interval - optional extensions This specification defines thefollowing definitive response indicators for use in the certificatestatus value: - good - revoked - unknown

In Table 4 above, the bold insertion shows additional information whichmay be provided in the status response.

Time at which OCSP Staples are Fetched

OCSP Staples may be fetched in various ways. One example is providedbelow with regards to FIGS. 12 and 13. However, the embodiments of FIGS.12 and 13 are merely provided for illustration, and other methods ofobtaining OCSP staples could be used with the embodiments of the presentdisclosure.

Therefore, in accordance with one embodiment of the present disclosure,in fetching OCSP staples, various factors may be taken into account. Onefactor may be to prevent peaks in load on the OCSP Responder server. Inthis regard, the load on the OCSP Responder server caused by clientsrequesting OCSP staples may be spread over time.

A further factor would be to ensure that the maximum time a vehicle canremain misbehaving is no worse than that which occurs when staples arenot used or cannot be accessed.

A further factor is to ensure that devices have plenty of time to gatherOCSP staples, noting that wide area network (WAN) connectivity may beintermittent in time.

Therefore, reference is now made to FIG. 12, which illustrates the casewhere a CRL update is provided every seven days, and a maximum time thata vehicle can be misbehaving is therefore seven days.

As seen in FIG. 12, a CRL is broadcast at time 1210 for week n, at time1212 for week n+1 and at time 1214 for week n+2. In this embodiment, adevice has a 3.5 day window in the half week period prior to the startof week n+1 in which to obtain the OCSP responses for the 20certificates that will be used in week n+1. However, these OCSPresponses expire at the beginning of the second half of the week n+1.This expiration is achieved by the OCSP responder setting the ‘responsevalidity interval’ in the OCSP response accordingly.

In this way, it can be ensured that a device will not be allowed tocontinue misbehaving for more than seven days from the time 1220 periodthat the OCSP response was obtained. In particular, at time 1220, adevice may obtain OCSP staples for the 20 certificates of week n+1 witha validity period set to cover the first half of week n+1.

Further, there is also plenty of time for the device to obtain the OCSPstaples prior to week n+1 starting. This may be achieved, for example,by obtaining a good WAN coverage opportunity.

By having an access delay 1222, the load of the OCSP server load can bespread over the 3½ days.

At some point in the first half of week n+1, the device again visits theOCSP responder to obtain a new batch of OCSP responses. The responseswill be received assuming the certificates associated with the devicehave not been placed on the CRL. In this regard, the device will beissued with the new batch of OCSP responses with a ‘response validityinterval’ set to be valid for the OCSP response expiring at the end ofweek n+1. Once again, a device may not be misbehaving for more thanseven days from the time 1230 in which the second set of OCSP stapleswas received for week n+1. Further, the load on the OCSP responder canbe spread over the 3.5 day period by using an access delay (n+1,1).

An ITS station receiving a certificate with the OCSP staple will notneed to determine the validity period of the long-term certificateitself. Assuming that the OCSP staple is received within its validityperiod, then the certificate will also be within its validity period. Aswould be appreciated by those skilled in the art, the two validityperiods, namely the validity period for the staple and the validityperiod for the certificate, are different.

If the ITS station receiving the V2X message receives an OCSP staple ata point in time which is not within the validity period of that OCSPstaple, then the receiving device can take an action such as discardingthe complete V2X message in some embodiments.

The device would obtain the period of the CRL issue and the time of thenew CRL issue from the IssueDate and nextCRL fields in a CRL, asdescribed for example the in IEEE 1609.2, section 7.3.2 Cr/Contentsmessage. In this way, a device may determine the absolute time frameworkaround which the present embodiment is based.

The access delay 1222 and the access delay 1232 are shown with respectto a half week boundary. One exemplary algorithm for determining at whatspecific times within the half week an ITS station should attempt toobtain certificates from an OCSP responder may be as follows.

An ITS station may build a historical record of the probability ofhaving IP connectivity during any one minute interval in a relevant halfof the week under consideration.

Referring to FIG. 13, a 20 minute window within the half week is shown.In practice this would be extended to the entire half week. In thisregard, a label, from one to 20, may be added to each minute segment.Further, one minute intervals having a probability greater than Px of IPconnectivity being available could also be labelled from 1 to N. Forexample, Px could be set to 0.4, indicating that a fairly good chance ofIP connectivity being available over that one minute interval exists.Based on FIG. 13, such intervals are identified with shading and arenumbered time intervals 1 to 8.

A pseudo random draw could then be made over N to determine a first setof one minute intervals during which an attempt to obtain certificatesmay be made. The pseudo random draw could be done, for example, byperforming a modulo operation on the linkage value in the firstcertificate that will be in use that week. Therefore, the first attemptat obtaining certificates will occur at a time interval LinkageValue(1,n) mod N.

While the probability of successfully obtaining certificates is lessthan Py considering all possible access attempts, where Py may be set toa value such as 0.85, then random draws could continue to be made toselect one minute periods during which the device will attempt to obtainOCSP responses. Each subsequent random draw could, for example, applythe modulo operation above, but using a different linkage value eachtime, taken from a different one of the 20 certificates that areapplicable in a given week. The identified periods are shown with starsin the embodiment of FIG. 13.

For example, it may be assumed that the probability of IP connectivitybeing available in some time slots is greater than 0.4, as shown withthe shaded squares in the embodiment of FIG. 13. For simplicity, in thepresent example the probability of IP connectivity in the shaded squaresis set to exactly 0.4 in these periods.

Further, in the example, an 85% chance of success (Py=0.85) is desiredin getting OCSP Responses at some point in this 20 time slot interval.In other words, a 15% chance of failure is acceptable in the example.

The test opportunities are shown with stars in the embodiment of FIG.13. In this case, if only one access opportunity exists, then the chanceof failure would be 6/10 (0.6). If two access opportunities wereprovided, then the chance of failure is 6/10*6/10=36/100 (0.36). Ifthree access opportunities are provided, then the chance of failure is6/10*6/10*6/10=216/1000 (0.216). If four access opportunities areprovided, then the chance of failure is 6/10*6/10*6/10*6/10=1296/10,000(0.1296).

Thus, with four access opportunities, there is less than a 15% chance offailure.

Therefore, the operation of the device in the example of FIG. 13 wouldbe as follows. The device would attempt to obtain an OCSP response intimeslot 3. If successful, then the OCSP responses are obtained and theprocess would end.

If unsuccessful at the timeslot 3, the device would attempt to get OCSPresponses at timeslot 6. If successful, then the OCSP responses areobtained and the process ends.

Otherwise, the process next attempts to obtain the OCSP responses attimeslot 14. If successful, the OCSP responses are obtained and theprocess ends. Otherwise the process would next attempt to obtain theOCSP responses at time slot 19.

In some embodiments, randomization of the time access within each oneminutes time interval could also be used. This could again be performedusing for example, a linkage value modulo Na, where the one minuteinterval is divided into Na subperiods. For example, Na may be 1000.This prevents multiple devices all attempting to access at the verybeginning of the one minute time slot.

Indication to a Receiver of a V2X Message that an OCSP Response isPresent in the V2X Message

In accordance with the embodiment of FIG. 10, a receiver of the V2Xmessage needs to know whether there is an OCSP response stapled to it ornot. This is used, for example, in the check at block 1020 of FIG. 10.

One option would be to create a new field, entitled “ocspStaple”, whichmay be added to the ToBeSignedCertificate as specified in IEEE 1609.2.This field may indicate that an OCSP response may or may not be stapledto the certificate.

If a V2X receiver reads the certificate and determines that an OCSPResponse may be stapled to the certificate, it can then determinewhether an OCSP Response has or has not been stapled to the certificate.This could be done by specifying that the, for example, first x bytes ofthe part of the message, which for example follows the certificate areto take a particular value if an OCSP Response has been stapled to thecertificate. The V2X receiver then reads the next x bytes following thecertificate and determines whether an OCSP Response has been stapled tothe certificate. The value x may be chosen to be sufficiently high thatthe probability of the sequence occurring by chance in a V2X messageformat in which there is no OCSP staple present is negligibly small.

As an alternative to reading the certificate and checking for theocspStaple field before searching for the presence of an OCSP Response,one embodiment may instead look directly for the presence of an OCSPResponse in a V2X message by looking for the specified x byte sequencein the V2X message. For example, this may be done using a correlationreceiver based approach.

Therefore, in accordance with the embodiments above, an indication maybe provided in a V2X message that a CRL check does not need to beperformed. The indication may be the presence of a short-livedcertificate, which may be indicated through various means, and maysignify to a receiving ITS station that the certificate was recentlyobtained and therefore is still valid. In other embodiments, theindication may be an OCSP staple that is added to the certificate toprovide an indication that no CRL check needs to be made.

As more vehicles become cellular connected and can obtain freshshort-lived certificates or OCSP staples, the processing and memoryburden associated with performing a check against a CRL for theequipment that needs to receive V2X messages will be reduced.

Enabling a fallback mode of operation, wherein a vehicle can transmitlong-lived certificates in situations where it has been unable to obtainthe required daily or weekly cellular or Wi-Fi connectivity to gathereither short-term certificates or short-lived OCSP responses, allows forflexibility in the solution.

Further, when utilizing short-lived certificates, there is backwardscompatibility where a long-lived certificate approach is deployed in thefirst generation of ITS stations. In this case, both long-livedcertificates and short-lived certificates can be supported in asecond-generation dual-mode ITS station. Specifically, first generationsingle mode ITS stations can still process short-lived certificates.

The use of short-lived certificates, where possible, solves anotherproblem for a message receiving vehicle which can occur when long-livedcertificates are used. This problem that can occur is that if thereceiving vehicle has been unable to obtain up-to-date CRL, then it hastwo options available, both of which have downsides. Either the vehiclemust discard the received messages, which reduces usefulness of the ITSsystem, or else the received message is used, but this comes with therisk that the message may actually be untrustworthy.

The ITS stations and network elements described above may be anycomputing device or network node. Such computing device or network nodemay include any type of electronic device, including but not limited to,mobile devices such as smartphones or cellular telephones. Examples canfurther include fixed or mobile user equipment, such as internet ofthings (IoT) devices, endpoints, home automation devices, medicalequipment in hospital or home environments, inventory tracking devices,environmental monitoring devices, energy management devices,infrastructure management devices, vehicles or devices for vehicles,fixed electronic devices, among others. Vehicles includes motor vehicles(e.g., automobiles, cars, trucks, buses, motorcycles, etc.), aircraft(e.g., airplanes, unmanned aerial vehicles, unmanned aircraft systems,drones, helicopters, etc.), spacecraft (e.g., spaceplanes, spaceshuttles, space capsules, space stations, satellites, etc.), watercraft(e.g., ships, boats, hovercraft, submarines, etc.), railed vehicles(e.g., trains and trams, etc.), and other types of vehicles includingany combinations of any of the foregoing, whether currently existing orafter arising.

One simplified diagram of a computing device is shown with regard toFIG. 14. The computing device of FIG. 14 could be any mobile device,portable device, network node, ITS station, server, or other node asdescribed above.

In FIG. 14, device 1410 includes a processor 1420 and a communicationssubsystem 1430, where the processor 1420 and communications subsystem1430 cooperate to perform the methods of the embodiments describedabove. Communications subsystem 1420 may, in some embodiments, comprisemultiple subsystems, for example for different radio technologies.

Processor 1420 is configured to execute programmable logic, which may bestored, along with data, on device 1410, and shown in the example ofFIG. 14 as memory 1440. Memory 1440 can be any tangible, non-transitorycomputer readable storage medium. The computer readable storage mediummay be a tangible or in transitory/non-transitory medium such as optical(e.g., CD, DVD, etc.), magnetic (e.g., tape), flash drive, hard drive,or other memory known in the art.

Alternatively, or in addition to memory 1440, device 1410 may accessdata or programmable logic from an external storage medium, for examplethrough communications subsystem 1430.

Communications subsystem 1430 allows device 1410 to communicate withother devices or network elements and may vary based on the type ofcommunication being performed. Further, communications subsystem 1430may comprise a plurality of communications technologies, including anywired or wireless communications technology.

Communications between the various elements of device 1410 may bethrough an internal bus 1460 in one embodiment. However, other forms ofcommunication are possible.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

While operations are depicted in the drawings in a particular order,this should not be understood as requiring that such operations beperformed in the particular order shown or in sequential order, or thatall illustrated operations be performed, to achieve desirable results.In certain circumstances, multitasking and parallel processing may beemployed. Moreover, the separation of various system components in theimplementation described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts.

Also, techniques, systems, subsystems, and methods described andillustrated in the various implementations as discrete or separate maybe combined or integrated with other systems, modules, techniques, ormethods. Other items shown or discussed as coupled or directly coupledor communicating with each other may be indirectly coupled orcommunicating through some interface, device, or intermediate component,whether electrically, mechanically, or otherwise. Other examples ofchanges, substitutions, and alterations are ascertainable by one skilledin the art and may be made.

While the above detailed description has shown, described, and pointedout the fundamental novel features of the disclosure as applied tovarious implementations, it will be understood that various omissions,substitutions, and changes in the form and details of the systemillustrated may be made by those skilled in the art. In addition, theorder of method steps are not implied by the order they appear in theclaims.

When messages are sent to/from an electronic device, such operations maynot be immediate or from the server directly. They may be synchronouslyor asynchronously delivered, from a server or other computing systeminfrastructure supporting the devices/methods/systems described herein.The foregoing steps may include, in whole or in part,synchronous/asynchronous communications to/from thedevice/infrastructure. Moreover, communication from the electronicdevice may be to one or more endpoints on a network. These endpoints maybe serviced by a server, a distributed computing system, a streamprocessor, etc. Content Delivery Networks (CDNs) may also provide mayprovide communication to an electronic device. For example, rather thana typical server response, the server may also provision or indicate adata for content delivery network (CDN) to await download by theelectronic device at a later time, such as a subsequent activity ofelectronic device. Thus, data may be sent directly from the server, orother infrastructure, such as a distributed infrastructure, or a CDN, aspart of or separate from the system.

Typically, storage mediums can include any or some combination of thefollowing: a semiconductor memory device such as a dynamic or staticrandom access memory (a DRAM or SRAM), an erasable and programmableread-only memory (EPROM), an electrically erasable and programmableread-only memory (EEPROM) and flash memory; a magnetic disk such as afixed, floppy and removable disk; another magnetic medium includingtape; an optical medium such as a compact disk (CD) or a digital videodisk (DVD); or another type of storage device. Note that theinstructions discussed above can be provided on one computer-readable ormachine-readable storage medium, or alternatively, can be provided onmultiple computer-readable or machine-readable storage media distributedin a large system having possibly a plurality of nodes. Suchcomputer-readable or machine-readable storage medium or media is (are)considered to be part of an article (or article of manufacture). Anarticle or article of manufacture can refer to any manufactured singlecomponent or multiple components. The storage medium or media can belocated either in the machine running the machine-readable instructions,or located at a remote site from which machine-readable instructions canbe downloaded over a network for execution.

In the foregoing description, numerous details are set forth to providean understanding of the subject disclosed herein. However,implementations may be practiced without some of these details. Otherimplementations may include modifications and variations from thedetails discussed above. It is intended that the appended claims coversuch modifications and variations. Further, the clauses below alsoprovide for aspects of the present disclosure.

AA. A method at a computing device within an Intelligent TransportationSystem, the method comprising: receiving a message signed with acertificate; checking for an indication within the message; andinspecting a Certificate Revocation List for the certificate only whenthe indication is absent from the message.

BB. A method at a computing device within an Intelligent TransportationSystem for sending a message, the method comprising: determining, at thecomputing device, whether an Online Certificate Status Protocol (OCSP)staple is available for a signing certificate at the computing device;if the OCSP staple is available: including the OCSP staple with in themessage; if the OCSP staple is not available, signing the message withthe certificate and without the OCSP staple; and sending the message toa recipient.

CC. A method at a network element in an Intelligent TransportationSystem, the method comprising: determining that a computing devicehaving at least one short-term certificate and at least one long termcertificate has been blacklisted for the at least one short-termcertificate or the at least one long term certificate; and blacklistingthe other of the at least one short-term certificate or the at least onelong term certificate.

DD. A method at a computing device in an Intelligent TransportationSystem, the computing device having at least one short-term certificateand at least one long term certificate, the method comprising:determining that one of the at least one short-term certificate and atleast one long term certificate has been blacklisted; and preventingcommunication from the computing device using the other of the at leastone short-term certificate and the at least one long term certificate.

EE. A method at a computing device for obtaining an Online CertificateStatus Protocol (OCSP) staple, the method comprising: finding aplurality of candidate time slots during which a probability of anetwork connection exceeds a threshold; randomly choosing a set from theplurality of candidate time slots, the set containing a subset of thecandidate time slots such that a probability of successfully obtainingcertificates during the set exceeds a second threshold; andprogressively attempting to obtain OCSP staples during the candidatetime slots within the set.

FF. The method of clause EE, wherein the randomly choosing is performedusing a modulo operation on a linkage value in a certificate on thecomputing device.

GG. The method of clause EE, wherein the obtaining is performed within aperiod which is half the period at which a CRL is issued.

HH. The method of clause EE, wherein the attempting occurs during arandom time within a selected candidate timeslot.

1. A method at a computing device within an Intelligent TransportationSystem, the method comprising: determining, at the computing device,whether a non-expired Online Certificate Status Protocol (OCSP) responsefor a certificate of the computing device is available; if thenon-expired OCSP response is available, signing the message with aprivate key associated with the certificate and appending the OCSPresponse; if the non-expired OCSP response is not available, signing themessage with the private key associated with the certificate; andsending the message to a recipient.
 2. The method of claim 1, whereinthe certificate is a long-term certificate for the computing device. 3.The method of claim 1, wherein the non-expired OCSP response isavailable if a non-expired OCSP response with a validity period that hasnot expired is stored at the computing device.
 4. The method of claim 1,further comprising determining that a network connection is available,and obtaining a non-expired OCSP response.
 5. The method of claim 1,wherein the OCSP response is obtained from a Security CredentialManagement System (SCMS).
 6. The method of claim 5, wherein the OCSPresponse is obtained by: sending a linkage value as an identifier to theSCMS; and receiving the OCSP response indicating that the linkage valuedoes not appear on a certificate revocation list.
 7. The method of claim5, wherein the OCSP response is obtained by: sending a Hash ID as anidentifier to the SCMS; and receiving the OCSP response indicating thatthe HashID does not appear on a certificate revocation list.
 8. Themethod of claim 5, wherein the obtaining includes a time delay to avoidoverloading the SCMS.
 9. The method of claim 1, wherein the non-expiredOCSP response provides an indication that the certificate was recentlychecked against a certificate revocation list and that the certificatedoes not need to be checked by a recipient of the message against acertificate revocation list.
 10. The method of claim 1, wherein thecertificate with the appended OCSP response is provided with themessage.
 11. A computing device within an Intelligent TransportationSystem, the computing device comprising: a processor; and acommunications subsystem, wherein the computing device is configured to:determine whether a non-expired Online Certificate Status Protocol(OCSP) response for a certificate of the computing device is available;if the non-expired OCSP response is available, signing the message witha private key associated with the certificate and appending the OCSPresponse; if the non-expired OCSP response is not available, signing themessage with the private key associated with the certificate; andsending the message to a recipient.
 12. The computing device of claim11, wherein the certificate is a long-term certificate for the computingdevice.
 13. The computing device of claim 11, wherein the non-expiredOCSP response is available if a non-expired OCSP response with avalidity period that has not expired is stored at the computing device.14. The computing device of claim 11, wherein the computing device isfurther configured to determine that a network connection is available,and obtaining a non-expired OCSP response.
 15. The computing device ofclaim 11, wherein the OCSP response is obtained from a SecurityCredential Management System (SCMS).
 16. The computing device of claim15, wherein the OCSP response is obtained by: sending a linkage value asan identifier to the SCMS; and receiving the OCSP response indicatingthat the linkage value does not appear on a certificate revocation list.17. The computing device of claim 15, wherein the OCSP response isobtained by: sending a HashID as an identifier to the SCMS; andreceiving the OCSP response indicating that the HashID does not appearon a certificate revocation list.
 18. The computing device of claim 15,wherein the computing device is configured to obtain the OCSP responseby including a time delay to avoid overloading the SCMS.
 19. Thecomputing device of claim 11, wherein the non-expired OCSP responseprovides an indication that the certificate was recently checked againsta certificate revocation list and that the certificate does not need tobe checked by a recipient of the message against a certificaterevocation list.
 20. A computer readable medium for storing instructioncode, which, when executed by a processor of a computing device withinan Intelligent Transportation System cause the computing device to:determine whether a non-expired Online Certificate Status Protocol(OCSP) response for a certificate of the computing device is available;if the non-expired OCSP response is available, signing the message witha private key associated with the certificate and appending the OCSPresponse; if the non-expired OCSP response is not available, signing themessage with the private key associated with the certificate; andsending the message to a recipient.